Building block



FIG. 1 is a perspective view of a building block showing my new design.

FIG. 2 is an end elevational view thereof.

FIG. 3 is a front elevational view thereof, it being noted that the rear elevational view is identical to the front elevational view in appearance.

FIG. 4 is a bottom plan view thereof. 

The ornamental design for a building block, as shown and described. 